Apparatus for transmitting voice frequencies over a single grounded line



Nov. 27, 1945. E. E. YORK APPARATUS FOR TRANSMITTING VOICE FREQUENCIES OVER A SINGLE GROUNDED LINE 2 Sheets-Sheet 1 Filed May 12, 1944 D2225 8 m m2:

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ATTORNEYS Nov. 27, 1945.

E. E. YORK APPARATUS FOR TRANSMITTING VOICE FREQUENCIES OVER A SINGLE GROUNDED LINE Filed May 12, 194-4 2 Sheets-Sheet 2 INVENTOR. ERNEST E. YORK ATTORNEYS Patented Nov. 27, 1945 APPARATUS FOR TRANSMITTING VOICE FREQUENCIES OVER A SINGLE GROUND- EDLINE Ernest E. York, Auburn, Maine, assignor to Stanley Dana Corp, Portland, Maine, a corporation of Maine Application May 12, 1944, Serial No. 535,243

6 Claims.

My present invention relates to apparatus for use in transmitting audio voice frequencies over single, grounded telegraph 'lines without interfering with the use of the telegraph instruments.

In certain organizations of which railroads afford one of the best examples, the stations, control towers, yard offices and other control points are generally serviced by a telegraph system to provide communication between such points. Telephones sometimes are also provided making it possible for the operator at any one control point to talk with the operator at another control point over existing telephone lines if the necessity arises.

It has been recognized for some time that such means of inter-location communication were not adequate because of insuflicient flexibility in service ofiered and in operation to meet all requirements. Among the desired factors may be noted the necessity of rapidity in communication, of communicating by voice simultaneously with several stations, and of having a system variable as to its power to ensure adequate transmission and reception under variable and adverse conditions.

In accordance with my invention, I provide apparatus consisting of a pre-amplifier and a main amplifier connected to a suitable power source. The transmitting circuit, connected to the telegraph line and its ground, includes a voice transmitted and the pre-amplifier, while the receiving circuit also connected to the telegraph line and its ground consists of a. voice filter, and voice receiver means. I provide switch mechanism to include the main amplifier either in the transmitting circuit or the receiving circuit to complete them and the telegraph line has bypass filters between stations and inductance coils at terminal stations to prevent voice currents from interfering with the normal use of the telegraph instruments.

Where the voice receiving circuit includes a voice receiver situated in a public part of a station, for example, I provide means for including such a voice receiver in the apparatus at the senders option.

In accordance with my invention, I, therefore, provide means by which any operator at any station can talk with Other stations without interference with telegraphic service while permitting him to control the receivers to be used. As the apparatus may be adjusted to ensure effective transmission and reception under any circumstances, my invention is well adapted to meet the requirements of inter-station or other interlocation communication.

In the accompanying drawings, I have shown diagrammatically an embodiment of my invention from which its novel features and advantages will be readily apparent.

In the drawings:

Fig. 1 shows diagrammatically an inter-location communication system in accordance with my invention, and

Fig. 2 is a similar View of the apparatus at each station.

At I0, I have indicated a single, grounded telegraph line having stations H at each of which are located telegraph instruments. As these may be conventional, I have not shown these instruments, but have indicated at l2 the usual telegraph line relay. I place bypass filters I3 in the line [0 between each of the stations II to prevent voice frequencies from interfering with the normal use of the telegraph instruments. At terminal stations, the line I6has inductance coils M to prevent voice currents from entering the circuits of the batteries I5.

Each of the locations or stations II is provided with audio transmitting and receiving apparatus. Such apparatus consists of a power supply generally indicated at I! and consisting of a transformer l8 and a power rectifier l9 having a circuit 26 and a circuit 2|.

The circuit 26 is the power supply circuit to a pre-amplifier 22 and a main amplifier 23, while the circuit 2| includes a relay 24 and a switch 25. The relay 24 is in control of 'switch mechanism generally indicated at 26.

One arm 21 of the switch mechanism 26 is adaptedto connect either the voice transmitting circuit 28 or the voice receiving circuit 29 to the main amplifier 23. The other arm 36 of the switch mechanism 26 is adapted to connect either the lead 3| or the receiver circuit 32 to the main amplifier 23.

The arms 21 and 36 are preferably positioned so that the apparatus at each of the stations H is in its receiving position with the circuit 29, which includes a voice filter 33 and is connected to the lead 3|, and the circuit 32, which includes one or more voice receivers such as the receivers 34 and loudspeaker 35 connected to the main amplifier 23. The circuits 29 and 32 may be regarded together as the voice receiving circuit when thus connected to the main amplifier 23.

The voice transmitting circuit 28 is shown as including a microphone 36 and the pre-amplifier 22, Preferably, I associate the switch 25 of the scribed, it will be apparent that the operator atany station I I may, by closing the switch 25, talk to any and all stations providedwith my apparatus and because of the bypass filters l3 and the voice filters 33, the line may be usedto carry voice frequencies without interference with or.

by the normal use of the telegraph instruments. My invention also permits the transmitting or receiving operator to vary amplification. as circumstances require.

In the apparatus thus far described, it will be apparent that the nature of. the voice; receiver or receivers is a matter of; choice. Where aloud: speaker-is used, particularlywhere it is located in a public part of the station, itisdesirable, to provide means for rendering it inoperative where confidential messages are, being transmitted.v I accomplish this result by arrangingv the. receivers3'4 and the loudspeaker 3.5.in parallel in the circuit 32 and between. them, I. provide a. switch 31 under the control of the telegraph relay l -2 'I-he transmitting operator is, accordinglyable to include the loudspeaker 35 in the circuit, 32 ateach station H by holding closed the key, of his telegraph instruments. My. apparatus may be'connected to the groundiof the'telegraph line or-toa second line if desired.

From the foregoing illustration of my invention, it will be apparent. that my invention is admirably adaptedtoa wide Variety of uses of which its combination with the telegraph system of a railroad isbut one example; Itmakes possible the-transmission of audio-voice frequencies over a single, grounded line and wherethatline has other uses such as aw telegraph line,- it: does notinterfere with the transmission of telegraphic messages simultaneously'with-the transmission of voice frequencies; It provides .simpleandreliable apparatus allowing voice communication with greater speed than is. possible with. conventional telephone systems. Ithas theadditional-advantages ofpermitting simultaneous. communicationwith several stations, variationsatieach star tionof thereceiving or transmitting power, and greater safety as-rproviding with thetelegraph system alternate means .ofcommunicationinthe event of failure of either system.

What-I therefore claim-and desire to secure-by Letters Patent is:

1. Apparatus for use at each station of a single, grounded telegraph line connecting telegraph instruments at each station, said apparatus comprising bypass filters between stations to bypass voice currents around said instruments to avoid interference with their use, inductance coils at terminal stations to prevent voice currents from entering battery circuits of terminal stations, a: pre,-amplifier, a main, amplifier, a power supply 'for; said amplifiers, an incomplete transmitting circuit connected to said line and to the ground thereof and including a voice transmitter andsaidpreramplifier, an incomplete receiving circuit. connected to said line and to said ground andincluding a voice filter and a voice receiver and switch means at each station to complete either'ofjsaid circuits by including said main amplifier therein.

2. In apparatus for use at each station of a single, grounded; line, said apparatus comprising, a. pre-amplifier, a main amplifier, a power supply for said amplifiers, an incomplete transmitting circuit; connected to said. line and to, the ground thereof and including" avoicetra-nsmitter and. said pre-amplifier; an; incomplete receiving circuit connected to, said line. and said ground and including a voice filter and a voice receiver, and switch means at; each. station. to. complete either of said, circuits; by including. saidmain amplifier therein.

3;. The apparatusoffclaim: l.in.- whichthe. switch meanshas; a-.normal position:inwhich: thev receiving circuit is completeanda: control. circuit comprising a SWltChifix relay, to operatethev switchto render the transmitting. circuit. complete. and.' the receiving circuit incomplete. I

4. The apparatus of claim, 2 and. means for varying the, power, to vary the. effectiveness of transmission or reception.

5. In apparatusfor use. ateachstation of. a single, grounded. telegraph line, connecting telegraphinstruments at eachstatiomsaid apparatus comprising apreeamplifier, a mainamplifier, a power. supply for. said amplifiers, an in.- complete transmitting circuit. connected to said lineand. to the ground. thereof. and, including a voice transmitter and said p're-amplifier, anincomplete receiving, circuitconnected to said'line and said ground andincluding a voice. filter, a voice, receiver, and a loud speaker, switch means to complete. either ofjsaidj circuits by. including said'main amplifier therein, and'means operable at the transmitting station to COIll'l6Ct'.0I" disconnect the loudspeaker from the receiving circult of the receiving station.

6". The apparatus of-claim 5 in whichthe voice receiver and the loudspeaker are in parallel in the receiving circuit and the receiving circuit includes a switch between the-receiverand the loudspeaker; and a telegraph relay operatesto close the switch; V

ERNEST E; YORK. 

